Understanding Extrusion 3E

263 Pages·2018·26.131 MB·English

by  Chris Rauwendaal

Rauwendaal
Understanding Extrusion

Chris Rauwendaal
Understanding Extrusion
3rd Edition
Hanser Publishers, Munich Hanser Publications, Cincinnati
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Dr. Chris Rauwendaal, 10556 Combie Road PMB 6677, Auburn, California 95602, USA
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Preface to the Third Edition
The first edition of Understanding Extrusion was published in 2000 and the second
edition in 2010. Since the second edition was issued several important develop-
ments have taken place. As a result, it makes sense to have a third edition of Under-
standing Extrusion.
Most of the new material is incorporated in Chapter 2. Topics included in this
chapter are interpretation of extrusion process data, dimensional variation by melt
temperature fluctuations, efficient extrusion, and more. Chapters 7 and 8 have also
been extended and now cover topics such as analysis of shrink void formation and
grooved barrel extruder technology.
I would like to thank Dr. Mark Smith for his encouragement to work on this third
edition. I also want to thank my wife Sietske for her continued support and for put-
ting up with me despite these time-consuming projects.
Chris Rauwendaal
September 2018
Contents
Preface to the Third Edition ........................................ V
1 Extrusion Machinery .......................................... 1
1.1 What is an Extruder? .......................................... 1
1.2 Different Types of Extruders .................................... 2
1.2.1 Single Screw Extruders .................................. 2
1.2.2 Twin Screw Extruders ................................... 2
1.2.2.1 Co-Rotating Twin Screw Extruders ................. 2
1.2.2.2 Counter-Rotating Twin Screw Extruders ............ 3
1.2.3 Ram Extruders ......................................... 4
1.3 Components of an Extruder ..................................... 5
1.3.1 The Extruder Screw ..................................... 5
1.3.2 The Extruder Barrel ..................................... 5
1.3.3 The Feed Throat ........................................ 6
1.3.4 The Feed Hopper ....................................... 7
1.3.5 Barrel Heating and Cooling .............................. 7
1.3.6 Screw Heating and Cooling ............................... 9
1.3.7 The Breaker Plate ....................................... 9
1.3.8 The Screen Pack ........................................ 10
1.3.8.1 Screen Changers ................................ 11
1.3.9 The Extrusion Die ...................................... 12
1.3.9.1 Coextrusion Dies ............................... 14
1.3.10 The Extruder Drive ..................................... 14
1.3.10.1 Coupling between Motor and Gearbox .............. 15
1.3.11 The Speed Reducer ..................................... 16
1.3.11.1 Thrust Bearing Assembly ........................ 16
1.3.12 The Gear Pump ......................................... 17
2 Instrumentation and Control .................................. 19
2.1 Instrumentation .............................................. 19
2.2 Most Important Process Parameters .............................. 19
2.2.1 Melt Pressure .......................................... 20
2.2.2 Pressure Transducers ................................... 21
VIII  Contents
2.2.3 Temperature Measurement ............................... 22
2.2.4 Melt Temperature Measurement .......................... 23
2.2.5 Barrel Temperature Measurement ......................... 24
2.3 Temperature Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.3.1 On-Off Control ......................................... 26
2.3.2 Proportional Control .................................... 26
2.3.3 Fuzzy Logic Control ..................................... 28
2.4 Collection and Interpretation of Extrusion Process Data ............. 29
2.4.1 Introduction ........................................... 29
2.4.2 Vital Signs of the Extrusion Process ....................... 29
2.4.2.1 Melt Pressure .................................. 30
2.4.2.2 Melt Temperature ............................... 35
2.4.2.3 Training ....................................... 44
2.4.3 Examples of Extrusion Problems Solved by Using a
Data Acquisition System ................................. 44
2.4.3.1 Variation in Stock Temperature ................... 44
2.4.3.2 Variation in Feed Housing Temperature ............ 46
2.4.3.3 Variation in Melt Pressure ........................ 48
2.4.4 Process Optimization .................................... 50
2.4.5 Temperature-Induced Dimensional Changes of Extrudate ..... 50
3 Complete Extrusion Lines ..................................... 53
3.1 Tubing and Pipe Extrusion Lines ................................ 53
3.2 Film and Sheet Lines Using the Roll Stack Process ................. 54
3.3 Film Lines Using Chill Roll Casting .............................. 55
3.4 Combination of Materials ....................................... 56
3.4.1 Coextrusion ........................................... 56
3.4.2 Extrusion Coating ...................................... 57
3.4.3 Extrusion Lamination ................................... 58
3.5 Blown Film Lines ............................................. 59
3.6 Extrusion Compounding Lines .................................. 59
3.7 Profile Extrusion Lines ......................................... 61
4 Plastics and Their Properties Important in Extrusion ............. 63
4.1 Thermoplastics and Thermosets ................................. 63
4.2 Amorphous and Semi-Crystalline Plastics ......................... 64
4.3 Liquid Crystalline Plastics (LCPs) ................................ 66
4.4 Elastomers ................................................... 66
4.5 Flow Behavior of Plastic Melts ................................... 67
4.6 Melt Index ................................................... 68
4.7 The Effect of Shearing ......................................... 69
4.8 Shear Thinning or Pseudoplastic Behavior ........................ 69
Contents  IX
4.9 Effect of Temperature on Viscosity ............................... 70
4.10 Viscous Heat Generation ....................................... 71
4.11 Thermal Properties ............................................ 71
4.11.1 Thermal Conductivity ................................... 72
4.11.2 Specific Heat and Enthalpy ............................... 72
4.11.3 Thermal Stability and Induction Time ...................... 73
4.11.4 Density ............................................... 74
4.11.5 Melting Point .......................................... 76
4.11.6 Glass Transition Temperature ............................ 76
5 How an Extruder Works ....................................... 77
5.1 Solids Conveying .............................................. 78
5.1.1 Gravity Induced Conveying ............................... 78
5.1.2 Drag Induced Conveying ................................. 81
5.1.3 Starve Feeding ......................................... 82
5.1.4 Grooved Feed Extruders ................................. 83
5.2 Melting ...................................................... 85
5.2.1 Contiguous Solids Melting ............................... 85
5.2.2 Dispersed Solids Melting ................................ 86
5.3 Melt Conveying ............................................... 89
5.3.1 Melt Temperatures ...................................... 90
5.4 Mixing ...................................................... 93
5.4.1 Distributive Mixing ..................................... 93
5.4.2 Mixing Sections ........................................ 98
5.4.2.1 Distributive Mixing Sections ...................... 98
5.4.2.2 Dispersive Mixing Sections ....................... 102
5.5 Degassing ................................................... 108
5.6 Die Forming .................................................. 110
5.6.1 Size and Shape Changes ................................. 111
5.6.2 Tubing and Pipe Dies ................................... 114
5.6.3 Flat Film and Sheet Dies ................................. 117
5.6.4 Profile Dies ............................................ 119
6 How to Run an Extruder ....................................... 123
6.1 Introduction .................................................. 123
6.2 Before Start-up ............................................... 123
6.3 Getting Ready for a Run ........................................ 124
6.4 Starting the Extruder .......................................... 126
6.5 Actual Operation .............................................. 128
6.6 Shutdown .................................................... 129
6.6.1 Purging ............................................... 129
6.7 Safety Issues ................................................. 131
6.7.1 Heat .................................................. 131
X  Contents
6.7.2 Moving Parts .......................................... 131
6.7.3 Electrical .............................................. 132
6.7.4 Weights ............................................... 132
6.7.5 Pressure .............................................. 132
6.8 Inspection and Training ........................................ 133
7 How to Troubleshoot Extrusion Problems ....................... 137
7.1 Objectives ................................................... 137
7.2 Prerequisites ................................................. 137
7.2.1 Good Instrumentation ................................... 137
7.2.2 Good Understanding of the Process ........................ 138
7.2.3 Collect and Analyze Historical Data ....................... 138
7.2.4 Teamwork ............................................. 138
7.3 Main Types of Problems ........................................ 139
7.3.1 Output Problems ....................................... 139
7.3.1.1 Low Extruder Output ............................ 139
7.3.1.2 Variation in Extruder Output ..................... 141
7.3.2 Appearance Problems ................................... 144
7.3.2.1 Lines ......................................... 145
7.3.2.2 Die Drool ...................................... 145
7.3.2.3 Discoloration and Degradation .................... 145
7.3.2.4 Voids ......................................... 147
7.3.2.5 Vent Flow ...................................... 156
7.3.2.6 Air Entrapment ................................. 156
7.3.2.7 Gels .......................................... 157
7.3.2.8 Poor Mixing .................................... 158
7.3.3 Functional Product Problems ............................. 160
7.3.4 High Melt Temperature .................................. 160
7.3.5 High Motor Load ....................................... 161
7.3.6 Wear Problems ......................................... 161
7.4 Systematic Problem Solving .................................... 163
7.5 Machine Troubleshooting and Maintenance ....................... 164
7.5.1 Check the Oil .......................................... 165
7.5.2 Unusual Noises ........................................ 165
7.5.3 Drive Motors and Belts .................................. 167
7.5.4 Spare Parts ............................................ 167
7.5.5 Screw and Barrel ....................................... 167
7.5.6 Extruder Maintenance Checklist .......................... 168
7.6 Troubleshooting Lists .......................................... 171
8 New Developments in Extrusion and Methods to
Increase Efficiency ........................................... 175
8.1 General Trends ............................................... 175
8.2 High-Speed Extrusion .......................................... 175